In modern medical science, in-vivo disease diagnosis is conducted using a variety of imaging equipments such as MRI, PET, CT or endoscopy, each of which having different scope of applications and advantages and disadvantages according to features thereof.
A medical imaging equipment proposed herein is similar to currently-available endoscope in terms of the fact that the equipment is capable of acquiring two-dimensional image of a specific site inside a human body or a site exposed to outside, using a probe for insertion into the human body or a long distance optical system having a long-working distance, while also providing real time-based qualitative analysis of multiple markers using marker nanoparticles binding thereto and signals. However, the proposed imaging equipment according to the present disclosure provides wider and more efficient range of applications than endoscopes. The advantages are obtained from a technology that simultaneously introduces multi signal components such as fluorescence and Raman signals (to be specific, SERS signals) for marker nanoparticles, along with an optical system which is capable of measuring the same with efficiency.
Endoscope non-invasively examines in-vivo the interior of organs such as digestive system or respiratory system. Diagnosis method using the endoscope is photodynamic diagnosis. Taking cancer diagnosis for example, invasive biopsy extracts biological sample and culture cancer tissue. However, optical biopsy using endoscopy does not require extraction of biological sample, but examines a suspected site by irradiating light. This method thus saves pains on the patient's side, and also offers convenience and simple process on the side of a practitioner who can use images. Additionally, endoscope offers advantages such as accurate cancer diagnosis and early detection of cancer.
Conventional endoscopic examination involves observation on mucous membrane using white light, using natural color representation of minute color shifting of mucous membrane to provide detection of minimal disease change which is as small as several millimeters. Meanwhile, the endoscopic investigation utilizing white light has insufficient ability to recognize dysplasia generally occurring in Barrett esophagus or to detect or diagnose colorectal polyp from non-tumor. Accordingly, biopsy and histopathologic examination are separately required, to characterize positivity of a sample or malignancy. However, biopsy has drawbacks mentioned above, and other shortcomings that it is prone to sampling error, or increased cost and lengthening time of inspection due to need for histopathologic examination.
Indeed, the white light-based endoscopic examination is considered to be a relatively simple screen technology, and it is not considered to be as technological as implied by the term ‘endoscopic imaging’ which generally refers to those technologies that illuminate artificial lights in-vivo to living organism and construct an image based on extraction/processing/interpretation of optical information that can be acquired from the living organism.
To compensate for the above-mentioned drawbacks, fluorescent imaging technology was proposed as the endoscopic imaging technology that utilizes fluorescence, according to which presence or absence of a targeted material can be analyzed with increased accuracy and in real time by distinguishing differences of colors or the like released from normal and abnormal structures with a diagnostic equipment, using autofluorescence which is naturally emitted from biological structure in response to a predetermined frequency of laser light emitted thereto, or photosensitizer or biomarker selectively remaining on a cancerous structure. The fluorescent imaging technology thus enabled in-vivo analysis of presence of targeted material on living organism, with increased accuracy and in a real-time basis (U.S. Pat. No. 7,285,089 et al.)
Fluorescence is used in a wide range of areas as a marker substance due to its high sensitivity that can detect even a single molecule. A considerable number of imaging technologies on marker materials have been proposed so far, including the in-vivo fluorescence imaging technology on marker material as proposed by Gambir et al. However, the fluorescence imaging technology has fundamental limitation particularly in terms of simultaneous detection on multiple biomarkers due to relatively wider bandwidth of the fluorescent spectra.
Accordingly, newer optical diagnostic technologies such as light scattering spectroscopy, or optical coherence tomography have been suggested so far, and attempts were continuously made to examine the states of the structures in details. The Raman spectrometry is gaining attention, as its way of detecting vibration spectra of molecules gives availability in a variety of optical fields and also it contains information about the structure of molecules. Since the Raman spectrometry basically enables characterization of biological constituents such as proteins or DNA based on the differences of molecular structures thereof. The Raman spectrometry is thus considered to be effective in the detection and diagnosis as to, for example, whether the polyp generated on mucous membrane is tumor or nontumor.
Raman scattering based on vibration of molecules has optical characteristics which are distinguished from the energy of incident light. Accordingly, Raman scattering has narrow line width, and different scattering wavelengths depending on the types and vibrations of the scattered molecules. Further, the Raman marker materials that express Raman scattering do not show photobleaching characteristic like fluorescence. By utilizing the above-mentioned optical characteristics, it will be possible to encode a plurality of biomarkers distinctively within a narrow optical region, and it is thus possible to detect signals from multiple biomarkers by single diagnosis performance and to perform diagnosis on molecular structure-based sample using the Raman spectrometry.
Many studies are currently conducted on the imaging analysis equipment which utilizes Raman spectrometry. By way of example, JP Patent Application Publication No. 2002-136469 (Reference 1) discloses an endoscopic apparatus employing a Raman spectrometer and an optical fiber, and JP Patent Application Publication No. 2009-511175 (Reference 2) discloses an imaging apparatus which achieves microimages using CARS signal.
However, many improvements are necessary to achieve accurate diagnosis by the Raman spectrometry utilizing endoscopy, because the Raman signal emitted from the sample itself is very weak, and most Raman signals are interfered with autofluorescence of the sample, thus causing difficulty of discriminating Raman spectra of normal site from those of abnormal site. That is, due to basically weak signal strength, the Raman signals are not easily detected due to various noises or fluorescence.
US Patent Application Publication No. 2008-0007716 (Reference 3) attempts to solve the problem of Raman signals being interfered with autofluorescence of a sample, by providing a method for removing fluorescent interference with a Shifted Excitation Raman Difference Spectroscopy (SERDS) system, but is not efficient enough to overcome the basic characteristic of the Raman signals, i.e., weakness of the signals. Further, most Raman spectrometry-based technologies suggested so far have not solved inconvenience of having to record spectra by scanning with individual optical fibers included in the optical fiber bundle and conduct imaging with respect to a specific band. Therefore, notwithstanding the advantageously narrow line width of Raman signals, practical utilization thereof for the simultaneous detection of multiple markers has limits.